Degreasing process



Patented Mar. 20, 1945 DEGREASING PROCESS Wilbur H. Petering, SouthCharleston, W. Va and Adam G. Aitchison, Westfleld,

N. 1., minors to Westvaoo Chlorine Products Corporation,

New York, N. Y.,

a corporationoi' Delaware No Drawing; Application October 1, 1942,

Serial No. 400,451 I 19 Claims.

This invention relates to an improvement in degreasing processesandother processes wherein chlorinated solvents are used as solvent media:and it comprises particularly a method of degreasing articles withsurfaces of a metal having a decomposing efiect'on chlorinated greasesolvents, such as aluminum goods, wherein grease is removed from such ametal surface by a. chlorinated solvent of a type normally subject tosuch decomposition, containing a minor amount of certainoxygen-containing organic compounds,

advantageously alcohols, which restrain such decomposition.

This application is a continuation-in-part of I our copendingapplication, Serial Number 386,544, filed April 2, 1941.

The removal of grease films from metal surfaces by. the application ofgrease solvents has been widely practiced during recent years. Numeroussolvents have been employed, and numerous variations of the degreasingprocedure have been suggested. In one method of operating, the metalarticle to be degreased is brought into contact with the solvent in theliquid phase. This may be accomplished by immersing the article in alarge body of the solvent, or by spraying the solvent on the surface ofthe article. In another common method of degreasing, known generally asvapor-phase degreasing, a body of solvent is maintained at the boilingpoint and in communication with a chamber adapted to contain a largebody of the solvent vapor. The article t be degreased is brought intocontact with this body of vapor, and causes condensation of the solventon the greasy metal surface. The condensed solvent removes grease andoil from the metal surface and drips on, usually returning to theboiling body of the solvent. With it goes dirt, et cetera, adhering tothe greasy surface. This dirt often includes metal chips, et cetera, Invapor-phase degreasers of this type, it is conventional to providecooling coils or some equivalent arrangement near the top of the solventvapor chamber to prevent or minimize the escape of vapors and loss ofsolvent from the system, Solvent condensed by such cooling. coils isgenerally substantially uncontaminated by either grease or dirt, and isusually returned to a clean solvent reservoir, which,in many cases, isarranged to overflow into the solvent boiling compartment. In somecases, even when employing vapor-phase degreasing, the article to bedegreased is preliminarily dipped in a body of liquid solvent. When hotsolvent is employed for this purpose, there is sometimes a subsequentdip in cooler solvent,

so that the article brought into contact with the solvent vapor willhave a sufliciently low temperature to cause the desired condensation ofsolvent on its surface in the vapor chamber.

As noted, numerous solvents have been employed in degreasing operations.Among these.

. solvents of. the chlorinated hydrocarbon type, in-

cluding both saturated compounds such as carbon tetrachloride, ethylenedichloride, et cetera, and unsaturated compounds such astrichlorethylene, perchlorethylene, et cetera, have been widely employedbecause of their high grease-solvent capacity and their lowinflammability. Several of these chlorinated compounds are considerednoninfiammable. Of the available solvents of this type, trichlorethyleneis probably most widely used in degreasing. However, it is seldom usedwithout the addition of some stabilizer," adapted to prevent or retardits decomposition during storage and normal use. This so-called normalltype of decomposition is promoted by light and oxygen, and their actionis accelerated by heat.

Several stabilizers are available and commonly used for the purpose ofinhibiting this decompo-.

sltion.

These previously known stabilizers are effective when present in minuteamounts in preventing decomposition of trichlorethylene: for example,during storage and during the usual degreasin operations applied toferrous metals and several ;other metals. However, when the metal to bedegreas'ed is aluminum or an aluminum alloy, or certain other metals notcontaining substantial quantities of aluminum, it has been found that aa different type of decomposition of, the solvent is encountered, andthat this type of decomposi tion may occur even in the presence ofstabilizers which are effective in all other cases. This form ofdecomposition of chlorinated solvents in contact with metallicaluminumor other metals having a. specific decomposing eflect on the solvent isevidenced by a rapid rise in acidity (largely hydrochloric acid), bypronounced discoloration of the solvent, and, in the advanced stages ofdecomposition, by the formation of a tarry or gummy mass in the solvent.

This type of decomposition takes place principally when the solvent isin the liquid phase and at elevated temperatures. It is most commonlyencountered in the boiling compartment of I a vapor-phase degreaserwhere, as previously noted, the solvent is maintained at the boilingpoint, and where thereis usually a collection of grease and finelydivided metal chips, filings, bufiings, et cetera, removed from themetal surfaces during treatment. When this accumulation includesturnings, chips, or other particles of aluminum (and to some extent,certain other metals) the described metal-induced decomposition is quitepronounced, unless special precautions are taken. This may beattributable, for example, to the catalytic or dechlorinating action ofaluminum and its compounds on the hot solvent Efforts have been madeheretofore to eliminate or minimize this type of decomposition byvarious special practices. In some instances, these practices have beenpartially successful, in that they have reduced formation of theabove-mentioned tarry and gummy masses from the solvent, for example.However, when such results have been obtained, they have beenaccompanied by undesirable results of other types, such as increasedacid development. It does not appear that prior to this invention therehas been any satisfactory solution to the problem of eliminating thespecial metal-induced type of decomposition encountered with thechlorinated solvents which are susceptible thereto. such astrichlorethylene, perchlorethylene, et cetera, when they are kept incontact with aluminum or other metals having a decomposing influence athigh temperatures.

The present invention is based on our discovery that this metal-induceddecomposition of chlorinated solvents, with production of hydrochloricacid and other deleterious decomposition products, is completelyprevented by the addition to the chlorinated hydrocarbon solvents ofcertain oxygen-containing organic compounds, such as organic oxides,oximes, ethers and alcohols. For instance, the aliphatic alcohols areparticularly suitable for this purpose and various monohydric andpolyhydric aliphatic alcohols may be advantageously employed as thestabilizer in the practice of this invention. Likewise, certainderivatives of these alcohols, such as amino-alcohols, mono-alkyl ethersof glycol, et cetera, may be employed with advantage in stabilizingchlorinated hydrocarbon solvents against metal-induced decomposition.

In particular. the monohydric aliphatic alcohols are very effectivestabilizers for chlorinated hydrocarbon solvents. As a class, thesealcohols have many advantageous properties which render themparticularly suitable for the present purposes. For instance,trichlorethylene and other unsaturated chlorinated hydrocarbon solventscontaining minor amounts of such alcohols are stable againstauto-oxidation, as well as metalinduced decomposition. Many of thesealcohols are volatile with the chlorinated hydrocarbons and protect thesolvent in the vapor phase; the alcohol remaining with the solvent whendistilled and condensed.

The monohydric aliphatic alcohols also have other advantages for thepresent purposes. First, as a class, they are readily soluble inchlorinated hydrocarbons and are completely compati ble with suchsolvents under service conditions. Under ordinary conditions they do notreact with the chlorinated hydrocarbons to form, sludge or otherdeleterious lay-products. Likewise, aliphatic alcohols do not attackmetals; they being neither alkaline nor acidic. In fact, the aliphaticalcohols are themselves substantially inert and stable under mostconditions. In other words, the aliphatic alcohols effectively stabilizechlorinated hydrocarbons without any deleterious acboth during storageand under service conons.

Thus, in preventing metal-induced deteriorzi:

tlon of chlorinated solvents (both saturated and unsaturated chlorinatedhydrocarbons), we usually employ aliphatic alcohols as the stabilizer.

In general, we have'found that the monohydric alcohols are moreeffective than the polyhydric alcohols for the purpose of thisinvention. Accordingly, we usually employ the monohydrlc alcohols in thepractice of this invention. In doing so, we have used bothstraight-chain and branch-chain alcohols and obtained effectivestabilization against metal-induced decomposition of the chlorinatedsolvents. With the primary aliphatic alcohols we have found thatstraightchain alcohols, such as ethanol, n-propanol, nbutanol, n-amylalcohol, n-hexanol, n-octanol, n-decanol, lauryl alcohol andheptadecanol, are particularly effective as stabilizers. Also primaryalcohols in which the aliphatic group is unsaturated, such as allylalcohol, et cetera, are also effective. Likewise, we have found thatbranchchain alcohols are also effective stabilizers and that theireffectiveness varies with the branching of the aliphatic chain. Forinstance, isobutanol, S-methylbutanol (isoamyl alcohol), 2-methylbutanol, Z-ethylhexanol and 2-ethylbutanol are all goodstabilizers. Likewise, secondary alcohols, such as l-ethylpropanol,l-methylbutanol and 1,3-dimethylbutanol, are good stabilizers againstmetal-induced decomposition but are not as effective as the primaryalcohols.

Tertiary aliphatic alcohols, such as tertiary amyl 46 propylene glycol,et cetera, are effective stabilizers. These dihydroxy aliphatic alcoholsmay be represented by the following general formula:

HO-R-OH 50 wherein R represents a divalent aliphatic group.

I the following generic formula wherein R represents an alkyl group,such as methyl, ethyl, propyl or butyl. As shown by the above formula,these stabilizers contain an alkoxy group attached to the aliphaticchain of a monohydric alcohol.

All of the stabilizers shown are aliphatic alco-' hols and as a classmay be represented by the following generic formula X-R-OH wherein Rrepresents a divalent aliphatic radical and X represents a substituentof the class consisting of alkyl, amino-alkyl, alkoxy and hydroxygroups, hydrogen and other substituents. That is, as the stabilizer, wemay employ aliphatic alcoacme hols carrying other substituents attachedto the aliphatic group. as well as the simple monohydric aliphaticalcohols.

However, our broad invention is not limited to the use 01 aliphaticalcohols as the stabilizer. We may also employ other oxygen-containingcompounds which are capable of preventing metalinduced decomposition ofchlorinated hydrocarbon solvents. For instance, various organic oxides,such as ethylene oxide, propylene oxide. dioxane, etc., are alsoeffective stabilizers and have been used in certain embodiments 01' ourinvention. Further, oximes, such as dimethyl glyoxime, alpha-benzyldioxime, acetaldoxime, acetoxime, et cetera, are also effective. oximesalso contain a hydroxyl group but it is attached to the nitrogen atom ofthe oxime. They may be used as the stabilizer and in fact they have beensuccessfully used in certain embodiments of our invention.

In the broad practice of our invention these oxygen-containing compoundsare generally employed in minor amounts, advantageously in the order of1 per cent of the amount of chlorinated solvent by weight. However, asthe eflectiveness of these stabilizers varies to some extent with thetype of compound employed, the particular percentage incorporated in thechlorinated hydrocarbon solvent maybe varied to obtain the stabilizationdesired. However, for purposes of the present invention, the morealcohol or other oxygen compound present, the more effective thecomposition in restraining this metal-induced" decomposition. Thisseemsto betrue because the oxygen compounds unite chemically with tiealuminum compounds that appear to cause the metal-induced decompositionand thus the more oxygen compound present the more stabilizationobtained. For "metal induced decomposition claimed in this applicationit is generally advantageous to use about 1 mol of oxygen compound per99 mols of chlorhydrocarbon. However, this.

amount may be, increased with proportionately reater stabilizationagainst metal-induced decomposition. If the solvent is used undercondi-' tions where both metal induced decomposition and auto-oxidationare encountered, the alcohol or other oxygenated compound must be usedin a balanced concentration -for optimum results.

That is, in the practice of our inventlommany and various embodimentsthereof may be employed. For instance, the chlorinated hydrocarbonsolvent, in addition to the stabilizers described, may also contain oneof the known stabilizers against normal-decomposition, as previouslymentioned, such as aralkyl ethers of hydroquinone, described in PitmanPatent 2,319,261.

In one useful embodiment of the invention, isoamyl alcohol is employedas the oxygen-com taining organic compound. This alcohol is especiallysuited for the purpose, because in small amounts it'forms aconstant-boiling mixture with trichlorethylene, and therefore tends toremain with the solvent, both as liquid and as vapor, during degreasingoperations and purification of the solvent in solvent-extraction,dry-cleaning, and similar operations. For example, on distilling thesolvent out of the boiling compartment of a vapor-phase degreaser topermit cleaning of this compartment, little, if any, of the alcohol islost. The alcohol evaporates and recondenses' with the solvent. It hasalso been found that isoamyl alcohol is highly effective in preventingthe metal-induced type of decomposition of trichlorethylene and similarchlorinated solvents,

These and its moderate cost is another favorable factor. Also,n-butanol, and n-hexanol are advantageous from the standpoint of,formation of these con-,

stant-boiling compositionaa't low concentrations 5 of alcohol, and, inpreventing metal-induced decomposition 0! chlorinated solvents. Ingeneral, the primary alcohols are most effective in preventing themetal-induced'decomposition. Secondary alcohols also produce goodresults. The tertiary alcohols are less effective. The polyhydricalcohols,such as the ethylene glycols and glycerine, also have asubstantial stabilizing effect, and are partlcularlyadapted for use withthe less volatile chlorinated solvents. In general, when working withany specific chlorinated solvent, it is desirable to employ'an alcoholorother oxygen-containing compound forming a mixture which may bedistilled without loss ofstabilizer.

Organic compounds having both alcoholic and amino characteristics may beemployed. The

aliphatic alcohol amines maybe used for this purpose, although somewhatlarger amounts are required than with the simpler and less expen-v sivealcohols. The compounds, 2-,aminoij2-methyl propane] and2-aminoblitanol, are soluble enough in chlorinated solvents tobe useiulalone; ,suffi: cient of them can be" dissolved injthe solvent to give 1the requireddeg'ree of stabilization Alcohols wit-bothersubstituentsthan the amino group may also be utilized. 1 j

- One specific advantage resulting from, theiaddltion orsuitablealcohols antifs'ijrnilar compounds to? chlorinated degreasingolve n'ts," as described hereinabovel isllithat the: once one minoramountbfox'ygn T 1, .n 'mscuni wit e resulting 1 decrease n metal-inducedecompose tion', pern its opration' of" the deer work durihg'thehegiieas the boiling point (or ife. boiling wmpamse"extent"thatreacti I rinated solvent and fine or other metal wineworlefi-ff lhis was liquid solvent h'asflarge ii whicharehighlyreactive;"espe ejia lly v creased boiling temperature .01 f,th'e"jdirtso It may'be thatwtheflqi e meta ana;

the *boiling *eql iparimggntnt "frequent?intervals. This 1 involvesadditiona ab'onflo of production during the: cleaning These difiicultiesf are ,1 ating' in accordance wi and it has-been foun ne' j qii. ment for a lonser perlodwithou the ecessit r degreasin operations inwhich hot chlorinated solvents a e employed.

In a specific example illustrative of a useful embodiment of the presentinvention, a decreasing solvent was prepared containing 99.0 parts byweight of stabilized trichlorethylene, and 1.0 part by weight of n-butylalcohol. .This solvent was used in a vapor-phase degreasing operation ofthe type previously described for degreasing aluminum surfaces.Naobiectionable decomposition was encountered, even after continuing theoperations without cleaning out the boiling compartment of the degreaserfor considerably longer than had been possible before the use ofalcohol, in accordance with this invention.

In the operation Just described, it was found that the alcohol vaporizedwith thetrichlorethylene, was condensed, and returned to the liquidcompartments with the trichlorethylene.

These chlorinated solvents, such as trichlorethylene, containing minoramounts of alcohols or other suitable oxygen-containing organiccompounds, are particularly adapted for use in degreasing aluminum andits alloys, and metals which tend to cause metal-induced decomposition,as described in our copending application, Serial Number 386,544. Suchsolvents are also useful in degreasing other metals, including zinc andmagnesium and their alloys as well as iron. steel, copper, et cetera,under conditions causing normal decomposition.

What we claim is:

1. As an improvement in degreaslngsurfaces of aluminum and it alloyswith chlorinated hydrocarbon solvents normally subject to deteriorationin the presence of aluminum, the improvement which comprisesmaintaining, in admixture with such chlorinated solvents, a minor amountof a monohydric aliphatic alcohol suillcient to inhibit suchmetal-induced decomposition thereof.

2. An improved process of degreasing surfaces of metals of the classconsisting of aluminum and its alloys having a decomposing 'eifect onchlorinated hydrocarbon grease solvents, which comprises contacting suchsurfaces with a chlorinated hydrocarbon grease solvent containing aminor amount of an aliphatic alcohol, said chlorinated hydrocarbonsolvent being normally subject to decomposition in contact with suchsurfaces and said aliphatic alcohol having the property of restrainingdecomposition of such solvents in the presence of said metal surfaces,the amount of said alcohol being sufllcient to inhibit suchmetal-induced decomposition of said chlorinated admixture therewith aminor amount of a monofl hydric aliphatic alcohol suflicient to inhibitthe said metal-induced decomposition thereof.

4. The improved process of degreasing surfaces of metals of the classconsisting of aluminum and proportion of oxygen-containing organic compound having the following formula K n-0H wherein R represents adivalent aliphatic radial and X represents a substituent of the classconsisting of hydrogen, alkyl, amino-alkyl, alkoxy and hydroxygroups andhaving the property of restraining decomposition of such solvents in thepresence of said metal surfaces, boiling said body of grease solvent andthereby maintaining a body of vapors thereof in said vapor space,contacting the metal surface to be degreased with said body of vaporsand returning the solvent condensed by said metal to said boiling. bodyof solvent, the amount ofsaid oxygen-containing compound in said body ofgrease solvent being sufficient to inhibit metal-induced decompositionthereof.

5. The method of claim 4 wherein said chlorinated hydrocarbon solvent istrichlorethylene.

6. The method of claim 4 wherein said oxygencontaining compound isn-butyl alcohol.

7. An improved method of degreasing surfaces of aluminum and its alloyswith chlorinated hydrocarbon solvents normally subject to decompositionin the presence of aluminum, which comprises contacting such metalsurface with a solvent composition comprising a chlorinated hydrocarbongrease solvent containing a minor amount of a monohydric aliphaticalcohol, the amount of said alcohol being sufllcient to inhibitmetalinduced decomposition of said chlorinated solvent.

8. The process of claim 7 wherein said alcohol is volatile with thechlorinated hydrocarbon solvent and the metal surfaces are contactedwith the solvent composition in the vapor phase.

9. An improved process of degreasing surfaces of aluminum and itsalloys, which comprises boiling a solvent mixture comprising a majoramount 0 of a chlorinatedhydrocarbon grease solvent, norits alloyshaving a decomposing effect on chlorinated hydrocarbon grease solvents,which comprises establishing a body of grease solvent in communicationwith a space adapted to receive vapors therefrom, said solventcomprising a major proportion of chlorinated hydrocarbon solvent,normally subject to decomposition, in the presence'of such mctalsurfaces, and a minor mally subject to decomposition in the presence ofaluminum, and a minor amount of aliphatic alcohol having the property ofpreventing decomposition oi such solvent in contact with such surfaces,contacting said metal surfaces with the vapors from the boiling solventmixture to cause partial condensation thereof, and returning solventcondensing on said metal surfaces to the boiling solvent mixture.

10. The method of claim 9 wherein said chlorinated solvent istrichlorethylene.

11. The method of cla m 9 wherein said alcohol is n-butyl alcohol.

12. The method of claim ,9 wherein said alcohol is isoamyl alcohol.

13. The method of claim 9 wherein said chlorinated solvent isperchlorethylene.

14. As an improvement in methods of degreesing surfaces of metals oftheclas consisting of aluminum and its alloys having a decomposingeffect on chlorinated hydrocarbon solvents, the improvement whichcomprises contacting such metal surfaces with a solvent compositioncomprising a chlorinated hydrocarbon grease solvent and a minor amountof an oxygen-containing compound having the following formula X-R-OHwherein R represents a divalent aliphatic radical and X represents asubstituent of the class consisting of hydrogen, alkyl, amino-alkyl,alkoxy and hydroxy groups and having the property of restrainingdecomposition of chlorinated hydrocarbon in the presence of said metals,the chlorinated hydrocarbon grease solvent being normally subject todecomposition in contact with such metal surfaces during decreasing andthe amount oi said oxygen-containing compound being suiflcient toprevent such metal-induced decomposition of the chlorinated solvent. I

15. The improved process of claim 14 wherein said oxygen-containingcompound is a monohydric aliphatic alcohol which is volatile with thechlorinated hydrocarbon grease solvent.

16; An improved process of decreasing suri'aces of aluminum and itsalloys, which comprises heating a solvent mixture containing a majoramount of a chlorinated hydrocarbon grease solvent and a minor amount ofan aliphatic alcohol, to a tem.

perature suflicient to evolve mixed vapors of chlorinated solvent andalcohol, contacting said vapors with said surfaces. condensing the mixedyapor in contact on said surface and returning cohol.

WILBUB H. PE'I'ERING. ADAM G. AI'iCi-IISON.

